Temp settings - red and blue zones?

[Rick Ohnsman]

In my '03 ST XLT it typically have the ventilation control set to bring in outside air, sometimes just through the upper vents, other times through the upper and floor vents, using the selector switch for that. (These are not the AC, or Max AC settings). However, I see that on the temperature setting dial there is a "blue zone" and a "red zone." It seems like even if I'm in the vent modes that if I turn the temp gauge into the blue zone, the air is colder than what I would expect if this were just outside air. Is the AC (or heat) coming on in these zones even if I'm not in one of the AC modes? Is the compressor running (and hence I'm hurting fuel economy?) With the price of fuel, I'm anxious to wring every drop for maximum efficiency. Right now I'm only getting between 14 and 15 mpg in normal in-town driving.

 

[Woppy V]

i think the compressor runs in all modes expect the floor vent...

 

[Jeffksf B]

If you have the owners manual it will tell you exactly what selections operate the A/C. I can't remember right now, I have to review it myself....

 

[JerryW Gilliland]

As far as I know, the AC compressor only runs when turned to AC settings.

My compressor makes a little noise when it kicks on and off, which I can hear.

Mine doesn't make that noise unless it's set on AC.

You can find out pretty easily by raising the hood with the engine running and the AC off and vent on.

Then get inside or have someone do it for you, and turn on the AC. You should hear the compressor come on. You can cycle it back and forth from off to on. There's a big difference in the sound when it's running.

 

[A K]

As far as I know, the AC compressor only runs when turned to AC settings.

It also runs on the defrost settings. This is so because to remove condensation, the air must be dry. Vent air often contains moisture, as opposed to the A/C, which does not.